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Wiring two LWCOs?

ranzerox Member Posts: 52
edited November 2022 in Strictly Steam
I have two LWCOs (Safeguard 400 and McDonnell & Miller Series 67), how do I wire them please? I'm looking for the Safeguard to be primary and both LWCO's use the VXT-24. Thanks


  • 109A_5
    109A_5 Member Posts: 1,387
    edited November 2022
    Hello @ranzerox,
    Basically both the Safeguard 400 and the VXT-24 units need 24 VAC power. Also so either the Safeguard 400 or the M&M 67 can call for a water feed the they have to be wired in parallel so either can activate the VXT-24. Additionally so either the Safeguard 400 or the M&M 67 can shut down the burner they have to be wired in series and in series with the burner and / or safety limit devices.

    The 'primary' is which ever unit is physically mounted higher on the boiler (the float or the probe), so as the water level drops it will activate that LWCO first. In this case it looks like it will be the Safeguard 400.

    This is one possible way without knowing more about the system you are working on.
    The jumper is installed between terminal 1 and P1 on the Safeguard 400.

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System